At room temperature, hot melt inks are generally in solid form. Upon exposure to the relatively high operating temperatures of an ink jet printer, hot melt inks liquefy. During application, minute ink droplets are sprayed onto paper or other similar material and immediately solidify upon impact with the printing substrate. Hot melt inks are beneficial since they exist in solid phase at room temperature, for example during transport or storage. Since the ink droplets, which are typically colored, instantly solidify upon impact with the material undergoing printing, running of the ink is precluded, which increases the quality of the print.
Previously employed hot melt inks are typically formulated for use at high printing temperatures, i.e. temperatures between 100 and 140.degree. C. Such high printing temperatures require high operating temperatures for the printing devices. High printing temperatures place high demands upon electronic components used in the printing devices. Accordingly, the life expectancy of such printing devices is not very long as a result of these extreme demands.
Low temperature hot melt inks have been developed. However, these inks exhibit low abrasion resistance and/or low adhesion to the printing substrate. Frequently, these inks separate from the printed material with normal handling such as bending or folding of the material. Furthermore, if the printed material is stored at temperatures which are only slightly above normal or ambient temperatures, the ink frequently sticks, for instance in the case of freshly printed paper, to the reverse side of the page on top.
Another, previously unsolved, problem is the relatively low transparency of colored hot melt inks during overhead projection of the printed material. Inks having poor transparency properties do not project vivid colors when used with overhead projection transparencies, for example. This problem is even more pronounced for low temperature hot melt inks. With low printing temperatures, the viscosity of the ink must be reduced. Lower viscosity is attained through increased addition of, for example, paraffin. Higher paraffin content, however, results in lower transparency of the resulting ink.